Damping factor switching in vehicle shock absorbers

Abstract

One or more vehicle suspension signals, preferably already generated within a controllable suspension system, is utilized to perform switches of the damping state of variable damping shock absorbers in the suspension system while the velocity of the shock absorbers is close to zero velocity. In particular, signals generated by height sensors within a controllable suspension system are utilized as vehicle suspension signals which are filtered to generate signals to enable switching of the shock absorbers while the shock absorbers are close to zero velocity. In addition, performance of the suspension system is improved by utilizing the vehicle suspension signals as one criterion to determine when switching from soft damping to firm damping or from firm damping to soft damping is desirable. Switch enable signals are determined from vehicle suspension signals by filtering at a resonant body frequency and comparison to an appropriate threshold. Soft-to-firm/firm-to-soft switch request signals are determined from vehicle suspension signals by filtering at a resonant wheel frequency and comparison to appropriate thresholds. Preferably, firm-to-soft switches are made after expiration of predefined time periods.

What is claimed is: 
     
       1. A method for operating a controllable vehicle suspension connected between a body and wheels of a vehicle, said method comprising the steps of: using a vehicle height signal as a vehicle suspension signal representative of the relative positioning of said body and at least one of said wheels;   passing said vehicle suspension signal through a bandpass filter centered on a body frequency of said vehicle to generate a body frequency signal representative of the velocity of the vehicle suspension at a body frequency;   comparing said body frequency signal to a first threshold for suspension jounce and a second threshold for suspension rebound;   generating a first switch request signal to request more firm damping in said vehicle suspension if said body frequency signal exceeds either of said first and second thresholds;   passing said vehicle suspension signal through a bandpass filter centered on a wheel frequency of said vehicle to generate a wheel frequency signal representative of the velocity of the vehicle suspension at a wheel frequency;   comparing said wheel frequency signal to a third threshold for suspension jounce and a fourth threshold for suspension rebound to determine whether the wheel frequency signal is between said third and fourth thresholds and therefor velocity of said controlled vehicle suspension is approximately equal to zero;   generating a switch enable signal while the velocity of said controlled vehicle suspension is approximately equal to zero to enable switching damping of said vehicle suspension;   combining said first switch request signal and said switch enable signal to generate a switch signal for switching to more firm damping in said vehicle suspension;   maintaining said more firm damping for said vehicle suspension for at least a defined time period;   generating a second switch request signal to request a change in said vehicle suspension to less firm damping upon expiration of said at least a defined time period; and   combining said second switch request signal and said switch enable signal to generate a switch signal for switching to less firm damping in said vehicle suspension.   
     
     
       2. A method for operating a controllable vehicle suspension connected between a body and wheels of a vehicle as claimed in claim 1 wherein said first threshold is larger than said second threshold. 
     
     
       3. A method for operating a controllable vehicle suspension connected between a body and wheels of a vehicle as claimed in claim 2 wherein said vehicle height signal is an existing signal generated by said controllable vehicle suspension for determining and adjusting the height of said vehicle such that an additional sensor is not required. 
     
     
       4. A method for operating a controllable vehicle suspension connected between a body and wheels of a vehicle, said vehicle suspension including a front vehicle suspension and a rear vehicle suspension, said method comprising the steps of: using a front vehicle height signal as a front vehicle suspension signal representative of the relative positioning of said body and at least one of said front wheels;   passing said front vehicle suspension signal through a bandpass filter centered on a body frequency of said vehicle to generate a front body frequency signal representative of the velocity of the front vehicle suspension at a body frequency;   comparing said front body frequency signal to a first threshold for suspension jounce and a second threshold for suspension rebound;   generating a front first switch request signal to request more firm damping of said front vehicle suspension if said front body frequency signal exceeds either of said first and second thresholds;   passing said front vehicle suspension signal through a bandpass filter centered on a wheel frequency of said vehicle to generate a front wheel frequency signal representative of the velocity of the front vehicle suspension at a wheel frequency;   comparing said front wheel frequency signal to a third threshold for suspension jounce and a fourth threshold for suspension rebound to determine whether the front wheel frequency signal is between said third and fourth thresholds and therefor velocity of said front vehicle suspension is approximately equal to zero;   generating a front switch enable signal while the velocity of said front vehicle suspension is approximately equal to zero to enable switching damping of said front vehicle suspension;   combining said first front switch request signal and said front switch enable signal to generate a front switch signal for switching to more firm damping in said front vehicle suspension;   maintaining said more firm damping for said front vehicle suspension for at least a defined time period;   generating a second front switch request signal to request a change in said front vehicle suspension to less firm damping upon expiration of said at least a defined time period; and   combining said second front switch request signal and said front switch enable signal to generate a front switch signal for switching to less firm damping in said vehicle suspension.   
     
     
       5. A method for operating a controllable vehicle suspension connected between a body and wheels of a vehicle as claimed in claim 4 further comprising the steps of: using a rear vehicle height signal as a rear vehicle suspension signal representative of the relative positioning of said body and at least one of said rear wheels;   passing said rear vehicle suspension signal through a bandpass filter centered on a body frequency of said vehicle to generate a rear body frequency signal representative of the velocity of the rear vehicle suspension at a body frequency;   comparing said rear body frequency signal to a first threshold for suspension jounce and a second threshold for suspension rebound;   generating a rear first switch request signal to request more firm damping of said rear vehicle suspension if said rear body frequency signal exceeds either of said first and second thresholds;   passing said rear vehicle suspension signal through a bandpass filter centered on a wheel frequency of said vehicle to generate a rear wheel frequency signal representative of the velocity of the rear vehicle suspension at a wheel frequency;   comparing said rear wheel frequency signal to a third threshold for suspension jounce and a fourth threshold for suspension rebound to determine whether the rear wheel frequency signal is between said third and fourth thresholds and therefor velocity of said rear vehicle suspension is approximately equal to zero;   generating a rear switch enable signal while the velocity of said rear vehicle suspension is approximately equal to zero to enable switching damping of said rear vehicle suspension;   combining said first rear switch request signal and said rear switch enable signal to generate a rear switch signal for switching to more firm damping in said rear vehicle suspension;   maintaining said more firm damping for said rear vehicle suspension for at least a defined time period;   generating a second rear switch request signal to request a change in said rear vehicle suspension to less firm damping upon expiration of said at least a defined time period; and   combining said second rear switch request signal and said rear switch enable signal to generate a rear switch signal for switching to less firm damping in said vehicle suspension.   
     
     
       6. A method for operating a controllable vehicle suspension connected between a body and wheels of a vehicle as claimed in claim 5 wherein said first threshold is larger than said second threshold. 
     
     
       7. A method for operating a controllable vehicle suspension connected between a body and wheels of a vehicle as claimed in claim 6 wherein said front vehicle height signal is an existing signal generated by said controllable vehicle suspension for determining and adjusting the height of the front of said vehicle, and said rear vehicle height signal is an existing signal generated by said controllable vehicle suspension for determining and adjusting the height of the rear of said vehicle such that additional sensors are not required.